The invention relates generally to epitaxial layers on biaxially textured surfaces and articles made therefrom. More specifically, the invention relates to a process for depositing epitaxial layers on biaxially textured substrates and associated articles.
Many device applications require control of the grain boundary character of polycrystalline materials which form part of the device. For example, in high temperature superconductors grain boundary characteristics are important. The significant effect of grain boundary characteristics on current transmission across superconductor grain boundaries has been clearly demonstrated for Y123. For clean, stoichiometric boundaries, the grain boundary critical current Jc (gb) appears to be determined primarily by the grain boundary misorientation. The dependence of Jc (gb) on misorientation angle has been determined by Dimos et al. [1] in Y123 for several grain boundary types, which can be formed in epitaxial films on bicrystal substrates. These include [001] tilt, [100] tilt, and [100] twist boundaries [1]. In each case, high angle grain boundaries were found to be weak-linked. The Jc value decreases exponentially with increasing grain boundary misorientation angle in artificially fabricated bicrystals of YBCO films [1]. The low Jc observed in randomly oriented polycrystalline Y123 can be explained by the small percentage of low angle boundaries, the high angle grain boundaries impeding long-range current flow.
Recently, the Dimos experiment has been extended to artificially fabricated [001] tilt bicrystals in Tl2Ba2CaCu2O8 [2], Tl2Ba2Ca2Cu3Ox [3], TlBa2Ca2Cu2Ox [4] and Nd1.85Ce0.15CuO4 [3]. In each case it was found that, as in Y123, Jc depends strongly on the distribution of grain boundary misorientation angles. Although no such measurements have yet been made on Bi-2223, data on current transmission across artificially fabricated grain boundaries in Bi-2212 indicates that most large angle [001] tilt [3] and twist [5,6] grain boundaries are weak links, with the exception of some coincident site lattice (CSL) related boundaries [5,6]. It is likely that the variation in Jc with grain boundary misorientation in Bi-2212 and Bi-2223 will be similar to that observed in the well characterized cases of Y123 and Tl-based superconductors. Hence in order to fabricate high temperature superconductors with very high critical current densities, it is necessary to biaxially align the grains to produce a high percentage of low angle grain boundaries. This has been shown to result in significant improvement in the superconducting properties of YBCO films [7-10].
A simple method to fabricate long lengths of textured substrates with primarily low-angle grain boundaries for epitaxial deposition of high temperature superconducting (HTS) materials was proposed by Goyal et al. [10]. This method is known as Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS). Four U.S. patents have been issued on this process and related process variants (U.S. Pat. Nos. 5,739,086, 5,741,377, 5,898,020 and 5,958,599). In the RABiTS method, the substrate formed has primarily low angle grain boundaries. A patent has also been issued on the fabrication of biaxially textured alloy substrates by Goyal et al. (U.S. Pat. No 5,944,966). An important issue in the successful use of alloy substrates in many applications is the ability to deposit high quality epitaxial buffer layers on the substrate.
References Cited:
1. D. Dimos, P. Chaudhari, J. Mannhart, and F. K. LeGoues, Phys. Rev. Lett. 61, 219 (1988); D. Dimos, P. Chaudhari, and J. Mannhart, Phys. Rev. B 41, 4038 (1990).
2. A. H. Cardona, H. Suzuki, T. Yamashita, K. H. Young and L. C. Bourne, Appl. Phys. Lett., 62 (4), 411, 1993.
3. M. Kawasaki, E. Sarnelli, P. Chaudhari, A. Gupta, A. Kussmaul, J. Lacey and W. Lee, Appl Phys. Lett., 62(4), 417 (1993).
4. T. Nabatame, S. Koike, O B. Hyun, I, Hirabayashi, H. Suhara and K. Nakamura, Appl. Phys. Lett. 65 (6), 776 (1994).
5. N. Tomita, Y. Takahashi and Y. Ishida, Jpn. J. Appl. Phys., 29 (1990) L30; N. Tomita, Y. Takahashi, M. Mori and Y. Ishida, Jpn. J. Appl. Phys., 31, L942 (1992).
6. J. L. Wang, X. Y. Lin, R. J. Kelley, S. E. Babcock, D. C. Larbalestier, and M. D. Vaudin, Physica C, 230,189 (1994).
7. Y. lijima, K. Onabe, N. Futaki, N. Sadakata, O. Kohno and Y. Ikeno, J. of Appl. Phys., 74, 1905 (1993).
8. R. P. Reade et al., Appl. Phys. Lett., 61, 2231 (1992).
9. X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter and D. E. Peterson, Appl. Phys. Lett., 65, 1961 (1994).
10. A. Goyal, D. P. Norton, D. M. Kroeger, D. K. Christen, M. Paranthaman, E. D. Specht, J. D. Budai, Q. He, B. Saffian, F. A. List, D. F. Lee, E. Hatfield, P. M. Martin, C. E. Clabunde, J. Mathis and C. Park, Special 10th anniversary on High Temperature Superconductors of J. of Materials Research, vol. 12, pgs. 2924-2940, 1997.
This invention provides a method for electrochemical deposition of epitaxial layers and formation of epitaxial articles. The method provides an inexpensive, non-vacuum technique that can proceed at a very high rate.
An epitaxial article is formed where at least one layer of the article is deposited using an electrochemical process. A substrate is provided having a biaxially textured surface. A substantially single orientation epitaxial layer deposited by an electrochemical process is disposed on and in contact with the biaxially textured surface.
A substantially single orientation epitaxial layer, as used herein, refers to a single orientation epitaxial layer having only one epitaxial crystallographic relationship with the surface in question. The substantially single orientation epitaxial layer preferably provides both in-plane texture and out-of-plane texture of less than 15 degrees FWHM, more preferably being less than 10 degrees FWHM.
The substrate can be a rolled and annealed biaxially-textured substrate having a biaxially textured metal surface. Textured metal surfaces can include Cu, Ag, Ni, Fe, Pd, Pt, Al, and alloys thereof. The substrate can also be a single crystal substrate. The substrate can be Si or GaAs, these substrates preferably being single crystal substrates.
The substantially single orientation epitaxial layer can be a metal or metal alloy layer, the metal or metal alloy layer selected from Cu, Ag, Ni, Fe, Pd, Pt and Al, and alloys thereof. The substantially single orientation epitaxial layer can provide both in-plane texture and out-of-plane texture of less than 10 degrees FWHM. At least one epitaxial buffer layer can be disposed on the substantially single orientation epitaxial layer.
The article can include an epitaxial electromagnetically active layer, such as a superconducting layer, disposed on and in contact with the epitaxial buffer layer. The superconductor layer can be an oxide superconductor. The oxide superconductor is preferably selected from REBa2Cu3O7 where RE is a rare earth element, and (Bi, Pb)1Sr2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4, (Tl, Pb)1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4, and (Hg, Tl, Pb)1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4. It is noted that (Bi, Pb) and (Tl, Pb) and (Hg, Tl, Pb) as used above imply any amount of doping of Pb, in (Tl, Pb) and (Bi, Pb) compounds and any amount of doping of Tl and Pb in (Hg, Tl, Pb) compounds. Furthermore, doping of Ca in RE for the REBa2Cu3O7 compound is also possible.
A method for electrochemically depositing epitaxial layers on substrates includes the step of providing a substrate with a textured surface. A substantially single orientation epitaxial layer is electrochemically deposited on the textured surface. The textured surface can be a metal surface, the metal surface preferably being biaxially-textured.
A biaxially-textured metal surface may be provided by rolling and annealing a metal material. Textured metal surfaces, preferably being biaxially-textured can be formed from rolling and annealing substrates such as Cu, Ag, Ni, Fe, Pd, Pt or Al, and alloys thereof. The substantially single orientation eiptaxial layer can also be a metal or metal alloy layer, the metal or metal alloy layer selected from Cu, Ag, Ni, Fe, Pd, Pt or Al, and alloys thereof. The substantially single orientation epitaxial layer can provide both in-plane texture and out-of-plane texture of less than 10 degrees FWHM.
The electrochemical deposition process can produce a deposition rate of at least 1 xcexcm/min and consist of either electroplating or electroless plating.
Improved epitaxial crystal quality can be obtained varying the deposition rate during the electrochemical deposition process, particularly by slowing the deposition rate which can otherwise increase over time. For example, the deposition rate can be varied by substantially suspending deposition during at least one interval during the time for the electrochemical deposition process. This can be accomplished by turning off the power supply in the case of an electroplating process.
The textured metal surface can be translated during the electrochemical deposition. For example, a reel-to-reel mechanism may be used for this purpose.
A method for electrochemically preparing an electromagnetically active epitaxial article includes the steps of providing a substrate with a textured surface, electrochemically depositing a substantially single crystal epitaxial layer onto the textured surface and depositing an electromagnetically active layer onto the substantially single crystal epitaxial layer. The textured surface is preferably biaxially-textured. Metal material can be rolled and annealed to form the biaxially-textured substrate, such as Cu. Ag, Ni, Fe, Pd, Pt, Al, or their respective alloys. The substantially single orientation epitaxial layer can also be a metal or metal alloy layer, the metal or metal alloy layer selected from Cu, Ag, Ni, Fe, Pd, Pt, Al, or their respective alloys. The substantially single orientation epitaxial layer can provide both in-plane texture and out-of-plane texture of less than 10 degrees FWHM.
At least one epitaxial buffer layer can be disposed on the epitaxial substantially single orientation layer, such as an epitaxial electromagnetically active layer or an epitaxial buffer layer. The electromagnetically active layer can be a superconducting layer, preferably an oxide superconductor.
The oxide superconductor is preferably selected from REBa2Cu3O7 where RE is a rare earth element, and (Bi, Pb)1Sr2Canxe2x88x921 CunO2n+2, where n is an integer between 1 and 4, (Tl, Pb)1Ba2Canxe2x88x921 CunO2n+3, where n is an integer between 1 and 4, and (Hg, Tl, Pb)1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4. It is noted that (Bi, Pb) and (Tl, Pb) and (Hg, Tl, Pb) as used above imply any amount of doping of Pb, in (Tl, Pb) and (Bi, Pb) compounds and any amount of doping of Tl and Pb in (Hg, Tl, Pb) compounds. Furthermore, doping of Ca in RE for the REBa2Cu3O7 compound is also possible. The electromagnetically active layer, such as a superconducting layer, can be deposited by an electrochemical deposition process.
At least one epitaxial buffer layer can be deposited on and in contact with the substantially single crystal epitaxial layer. An electromagnetically active layer, such as a superconductor layer can be disposed on the epitaxial buffer layer. In this embodiment, the superconducting layer is preferably an oxide superconductor.